Portable x-ray generating machine

ABSTRACT

A portable X-ray generating machine including an X-ray tube and a spiral generator power source in which the dimensions and positioning of the spiral generator are selected so that the generator encircles or surrounds the X-ray tube to form a compact unit. The spiral generator is formed from conductive sheets or foils which have a high coefficient of adsorption of X-radiation so that an operator will be effectively protected from Xradiation by the generator during operation of the tube. The portable combination of this invention is thus extremely light because a minimum of separate shielding material is needed. In the preferred embodiment illustrated herein of this invention, the electrodes of the X-ray tube are connected to the foils of the spiral by extremely short, well insulated paths. The short path lengths provide minimum inductance and thereby allow maximum voltage to be developed across the X-ray tube during the transient discharge, when the time rate of change in current is extremely high.

United States Patent Courtois [54] PORTABLE X-RAY GENERATING MACHINE [72] Inventor: Donald A. Courtois, Ypsilanti, Mich.

[731 Assignee: The Bendix Corporation [22] Filed: May 18, 1970 [21] App1.No.: 38,261

Robison ..250/98 5] Feb. 15, 1972 Primary ExaminerAnthony L. Birch Attorney-William F. Thornton and Plant, Hartz, Smith and Thompson [57] ABSTRACT A portable X-ray generating machine including an X-ray tube and a spiral generator power source in which the dimensions and positioning of the spiral generator are selected so that the generator encircles or surrounds the X-ray tube to form a compact unit. The spiral generator is formed from conductive sheets or foils which have a high coefiicient of adsorption of X-radiation so that an operator will be effectively protected from X-radiation by the generator during operation of the tube. The portable combination of this invention is thus extremely light because a minimum of separate shielding materia1 is needed. In the preferred embodiment illustrated herein of this invention, the electrodes of the X-ray tube are connected to the foils of the spiral by extremely short, well insulated paths. The short path lengths provide minimum inductance and thereby allow maximum voltage to be developed across the X-ray tube during the transient discharge, when the time rate of change in current is extremely high.

4 Claims, 2 Drawing Figures PORTABLE X-RAY GENERATING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention X-ray technology.

2. Description of the Prior Art Approximately 90,000 to 100,000 volts are needed to operate an X-ray tube. The problem of insulating a voltage of such magnitude has limited the development of portable X-ray tube units. One known portable unit includes a housing containing a Marx generator placed alongside and a slight distance away from an X-ray tube. The X-ray tube and generator are connected by a thick, coaxial cable capable of transmitting high voltages without melting or breaking down. The cable, X-ray tube, and generator are highly insulated to prevent the voltage from shorting or reaching an operator. A lead shield is placed around the sides of the X-ray tube to prevent X-radiation from reaching and harming an operator. The lead shield is necessary because an X-ray tube generates the same amount of X-radiation in substantially all directions. The lead shield is placed to absorb all radiation that would reach some point other than the object being X-rayed during normal operation of the tube.

SUMMARY OF THE INVENTION The portable X-ray tube and generator unit of this invention is smaller, lighter, and safer to operate than prior art devices. The unit comprises an X-ray tube which is surrounded or encircled by a spiral generator. A spiral generator is a known device for generating large voltages that comprises two sheets or foils of electrically conductive material and two sheets or foils of electrically insulative material arranged alternately and wound into a cylindrically shaped roll to form two openended strip transmission lines having a sheet of electrically conductive material in common. The two conductive foils will be referred to herein as the inner and outer conductive foils with the outer foil being the foil whose outermost turn has a larger diameter than the outermost turn of the other foil. The roll is wound to have an inner diameter which is larger than the diameter of the X-ray tube so that the tube can be placed inside the core of the generator. The subject portable X-ray tube and spiral generator unit is thus smaller than prior portable units because the generator surrounds and thus forms a portion of the housing for the X-ray tube. In the preferred embodiment illustrated herein, the conductive foils of the generator are formed from thin copper strips, a material that has a high coefficient of absorption for X-radiation. Since the spiral generator surrounds the X-ray tube, it protects an operator from X-radiation during operation so that only a minimum of separate X-ray shielding is needed with this invention. The subject unit is therefore lighter than previous devices both because the spiral generator eliminates the need for much of the separate X-ray shielding that must be included in other devices, and also because spiral generator power sources are lighter than the types of power sources previously used with X-ray tubes. The anode of the X-ray tube is connected to the innermost end of the outer conductive foil of the spiral generator, and the cathode of the X-ray tube is connected to the opposite or outermost end of that foil. A power source constructed to provide a negative charging potential is connected to the inner conductive foil of the spiral generator.

In operation, the outer foil of the spiral generator is maintained at ground potential while the inner conductive sheet is charged to a preselected negative voltage. This charging voltage has a substantially smaller value than the high-voltage output of the spiral generator. For example, the spiral generator illustrated in the preferred embodiment of this invention produces a 100,000-volt output pulse when supplied with a 10,000-volt charging potential. A high-voltage pulse is produced by shorting the inner and outer sheet of the spiral generator. This shorting produces a transmission wave which propagates between the conductive foils of the spiral generator and produces an extremely high voltage between the inner and outer ends of the two conductive foils for a very short period of time. This high voltage is applied to the electrode of the X-ray tube. Since the X-ray tube is disposed within the core of the spiral generator, the current need travel only a very short distance to reach the X-ray tube. The inductance of an electrical path, and therefore the voltage drop that occurs during the transient discharge is directly related to the length of that path. The subject invention minimizes losses and provides a very high-operating efficiency by minimizing the length of the path between the X-ray tube and the spiral generator.

The surface of the spiral generator, that is, the outermost turn of that outer foil of the spiral generator, remains at ground potential throughout operation of this invention. The outer surface of the spiral generator and the lead from that outer surface which connects the spiral generator to the cathode of the X-ray tube are thus safe surfaces which do not carry any high voltages which could be potentially dangerous to an operator. The high-voltage output of the generator is provided only at the inside edge of the spiral generator and travels only to the anode of the X-ray tube disposed inside the core of the spiral generator. The subject portable unit is thus safer to operate than are prior art devices because the arrangement of the X-ray tube and spiral generator effectively isolates and insulates that high voltage from an operator.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features and advantages of this invention, which are defined by the appended claims, will become apparent from a consideration of the following description and the accompanying drawings in which:

FIG. 1 is a plan, cross-sectional, longitudinal view of an embodiment of the portable X-ray tube and spiral generator combination of this invention; and j FIG. 2 is a circuit diagram of the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 illustrate a portable X-ray generating machine 10 which includes an X-ray tube 12 encircled by a spiral generator 14. The spiral generator is formed from an outer copper foil 16 and an inner copper foil 18 wound to form a cylindrical roll. The copper foils are each 0.003 inches thick and are separated and electrically insulated from each other by sheets of polyester film 0.004 inches thick. The foils are wound to form a generator having 60 turns. The drawings show a somewhat schematic view of the spiral generator in that only a few turns or layers of the copper foils forming the spiral generator are shown. The insulating polyester films which separate the copper foils are not shown. It is believed that the inclusion of such detail in the drawing would not aid the reader, but would instead detract from the invention which lies in the combination and arrangement of elements. The innermost end of the outer copper foil 16 is connected to the anode 20 of the X-ray tube 12 by a buss bar 22 and a copper line 24. The outer end of copper foil 16 is connected to the cathode 26 of the X-ray tube by a copper line 28 and finger contacts 30. The inner foil 18 is connected by cable 31 to a power source 32 which provides a charging voltage to that foil. In theory, the spiral generator will produce a peak output voltage equal to two times the charging voltage times the number of turns in the spiral generator roll. In practice, while extremely high voltages have been produced, the actual output is somewhat less than this theoretical value. The 30-turn spiral generator of this embodiment produces an output voltage pulse on the order of 100,000 volts when supplied with a I0,000-volt charging potential. Both the X-ray tube 12 and spiral generator 14 are surrounded and held by a molded, dielectric, resin housing 34 which holds those two elements and also acts to electrically insulate them from each other. The housing 34 also holds a spark gap switch 36. The opposite sides of the switch 36 are connected to the copper foils l6 and 18 so that when a voltage pulse is supplied to switch 36 along line 38, this switch provides a closed circuit between the two copper foils 16 and 18 and thus triggers the operation of the spiral generator 14.

In operation, the inner copper foil 18 of spiral generator 14 is charged to a negative ten thousand volt potential. The charging of foil 18 does not affect foil 16 which remains at ground potential. A voltage pulse is then supplied to switch 36 to short foils l6 and 18 and thus trigger operation of the spiral generator. A transmission wave propagates back and forth along the open-ended transmission line formed by the windings 16 and 18 and produces a high-voltage pulse on the order of 100,000 volts between the inner and outer ends of the windings l6 and 18. During the pulse a high current flows from winding 16 along buss bar 22 and line 24 to the anode 20 of the X-ray tube, through the tube, and back tothe spiral through cathode connections 28 and 30. The propagation of the transmission wave and generation of this high-voltage pulse at the inner end of the foils l6 and 18 does not affect the potential of the outermost turn of foil 16 which remains at ground potential during operation of the device. The high voltage needed to operate the X-ray tube is thus effectively isolated from an operator by the surrounding generator 14. The high voltage supplied to the anode 20 causes electrons to flow to that anode from the cathode 26, which is at ground potential. Electrons striking the anode 20 generate X-rays which travel in all directions from the surface of the anode 20. However, the copper windings of the generator 14 absorb X- rays which are emitted toward the sides of the generator so that radiation will be directed only through window 39 in X- radiation shield cap 40 toward an object being examined. An operator is thus effectively protected from X-radiation. Measurements show that the illustrated spiral generator, which possesses a thickness of 0. l 80 inches of copper on each side of the X-ray tube, will absorb 98 percent of X-radiation striking the surface of that generator. Less than one-fiftieth of the X- radiation which would normally be present at a similar distance from the anode of the X-ray tube, if that tube were not surrounded by a spiral generator or any other shielding, will be present at the surface of the illustrated spiral generator.

Having thus described one embodiment of this invention, a number of modifications will be immediately obvious to those skilled in this art. For example, the option of connecting the opposite ends of one conductive foil, namely, the outer conductive foil to the X-ray tube and charging the inner foil to a negative potential was selected so that the outer surface of the spiral generator could be maintained at ground and a highvoltage pulse of positive polarity would be provided at the inner end of the conductive windings by triggering the generator. If it is either unnecessary or undesirable to satisfy these requirements in another embodiment of this invention, the manner in which the X-ray tube is connected to the spiral generator, the polarity of the charging voltage, the foil to which the charging voltage is supplied, or any combination of the above can be varied from that shown in the illustrated embodiment.

Therefore, what is claimed is:

1. An X-ray generating machine comprising:

an X-ray tube having an anode and a cathode;

a spiral generator power source formed from two conductive foils that are electrically insulated from each other and wound to form a cylindrical roll comprising an openended transmission line, said spiral generator power source having an inner diameter larger than the outer diameter of the X-ray tube, and placed to encircle said X- ray tube; and

electrical conducting means connecting said generator and said X-ray tube to supply an operating voltage to said X- ray tube from said spiral generator.

2. The combination set forth in claim 1 further including means for triggering the operation of said spiral generator power source, said spiral generator encircling at least a portion of said triggering means.

3. The combination set forth in claim 2 in which: said conducting means connects said X-ray tube anode to the innermost end of the outer one ofsaid two conductive foils, and connects said X-ray tube cathode to the outermost end of said outer conductive foil; and

in which said combination further includes a power source connected to supply a negative charging voltage to the inner one of said two conductive foils.

4. The combination set forth in claim 3 in which said two conductive foils are formed from a conductive material having a high coefficient of absorption for X-radiation. 

1. An X-ray generating machine comprising: an X-ray tube having an anode and a cathode; a spiral generator power source formed from two conductive foils that are electrically insulated from each other and wound to form a cylindrical roll comprising an open-ended transmission line, said spiral generator power source having an inner diameter larger than the outer diameter of the X-ray tube, and placed to encircle said X-ray tube; and electrical conducting means connecting said generator and said X-ray tube to supply an operating voltage to said X-ray tube from said spiral generator.
 2. The combination set forth in claim 1 further including means for triggering the operation of said spiral generator power source, said spiral generator encircling at least a portion of said triggering means.
 3. The combination set forth in claim 2 in which: said conducting means connects said X-ray tube anode to the innermost end of the outer one of said two conductive foils, and connects said X-ray tube cathode to the outermost end of said outer conductive foil; and in which said combination further includes a power source connected to supply a negative charging voltage to the inner one of said two conductive foils.
 4. The combination set forth in claim 3 in which said two conductive foils are formed from a conductive material having a high coefficient of absorption for X-radiation. 